China Mobile Multimedia Broadcasting (CMMB) uses the mobile TV receiving standard STiMi, which is applicable to broadcast service frequencies in the frequency range of 30 MHz to 3000 MHz, the CMMB is a broadcasting system which transmits multimedia signals such as television, broadcast and data information via satellite and terrestrial radios and can achieve nationwide roaming. The CMMB uses two sets of receiving systems to support the U-band (470 MHz˜798 MHz) and S-band (2635˜2660 MHz) simultaneously, the U-band receives signals from the terrestrial forwarding networks, and the S-band receives TV broadcast signals from the satellites.
Currently, all the CMMB terminal schemes use separate antennas to achieve the CMMB reception, this is because the communication frequency band of the mobile terminals is very close to the frequency band of the CMMB, the sideband noise of the mobile communication module will fall in the CMMB receiving frequency band, and generate interference with the CMMB reception, thereby affecting the reception sensitivity, and leading to bit errors in the received programs, especially it has a greater impact on the CMMB reception because the transmitting frequency band (880 MHz˜915 MHz) of the global system for mobile (GSM) 900 is very close to the U receiving frequency band (470 MHz˜798 MHz) of the CMMB, and according to the stray testing standard in the 3GPP protocol, the minimum stray requirements of the GSM900 in the U-band is −36 dBm@3 MHz, the U-band receiving sensitivity of the CMMB is required to be higher than −95 dBm@8 MHz, the co-channel interference is required to be less than 9.2 dB, then it can be derived that the co-channel interference should not be greater than −85.8 dBm@8 MHz; considering that the sideband noise generated by the GSM900 transmission in the U-band is −36 dBm@3 MHz in the worst case, it is far beyond the co-channel interference acceptable by the CMMB.
In addition, the personal communications services (PCS) 1900 transmitting frequency band (1850 MHz˜1910 MHz) is also very close to the S receiving frequency band of the CMMB and has an impact on the S-band reception of the CMMB, but the impact is slightly smaller compared to the GSM900; in order to lower the interferences in these frequency bands, currently the common practice is to use separate antennas in the CMMB and the communication module to implement spatial isolation, so as to prevent the CMMB from the co-channel interference by improving the spatial isolation. However, this mode increases the difficulty of structural design, and its hardware cost is relatively high.